Recently, a technique for coupling between an in-vehicle information device and a mobile information terminal such as a smart phone via communication in cooperation with each other becomes popular (for example, a terminal mode, a name of which is changed to a mirror link (registered trademark) afterwards). An information display system described in Patent Literature No. 1 is well-known as this type of technique. In the information display system, display data displayed on a screen of a cell phone is supplied to an in-vehicle device, so that the display data is displayed on a display of the in-vehicle device. Further, a touch switch of the cell phone is displayed on the display of the in-vehicle device, and it is possible to operate the cell phone from the in-vehicle device using the touch switch.
The above technique provides to utilize a function of the mobile information terminal in the in-vehicle information device such that, for example, in the in-vehicle information device not having a navigation function, a map image provided by the navigation function of the mobile information terminal is displayed on the display of the vehicle.
Here, the mobile information terminal such as the smart phone may have a power saving mode for reducing electric power consumption in order to extend a working time of a built-in battery by limiting a part of the functions compared with a normal mode operation. The main functions of the above power saving mode include a function for reducing the electric power consumption by limiting the display operation of the display. For example, when no operation is performed for a predetermined time interval, the mobile information terminal is switched to the power saving mode, and the image display operation is terminated.
However, when the mobile information terminal stops displaying an image due to the power saving mode, the in-vehicle information device, which has displayed the image in cooperation with the mobile information terminal, has a problem of a waste of consuming the electric power because the in-vehicle information device continues operating the display even if the device lacks the image to be displayed. Specifically, it is very important to save an electric power for a vehicle such as an electric vehicle a hybrid vehicle and a plug-in hybrid vehicle, which runs with an electric power accumulated in a secondary battery. Thus, it is necessary to contrive a way for reducing the waste of electric power consumption.
However, in a conventional technique described in Patent Literature No. 1, the above described problem cannot be solved since it is not considered that the display operation of the display on the vehicle side is limited in cooperation with the in-vehicle information device when the mobile information terminal is switched to the power saving mode.